getting the most out of tracking vs memory
More tracking points are not better, but accurate ones are. More inaccurate trackers will only make things worse, not better.

The automatic feature detection sounds good in theory, but I still prefer choosing the tracking points myself, focusing on what items will be in frame for the longest time in the scene and which will help blender determine the 3d space.

To get better performance, let blender cache the  whole shot into RAM. You might need to increase the cache size in the system preferences.



For more tips on motion tracking please read: https://blender.stackexchange.com/a/42332/1853